U.S. patent number 4,197,857 [Application Number 05/894,189] was granted by the patent office on 1980-04-15 for system for measurement of oxygen uptake and respiratory quotient.
This patent grant is currently assigned to Research Development Corporation. Invention is credited to John J. Osborn.
United States Patent |
4,197,857 |
Osborn |
April 15, 1980 |
System for measurement of oxygen uptake and respiratory
quotient
Abstract
A system for measuring the oxygen uptake and respiratory
quotient of a patient which employs a high resistance gas flow path
in parallel with a pneumotachograph. The high resistance path is
connected to each side of the pneumotachograph and a small chamber
is included in the high resistance path at each end thereof
adjacent its connection to the pneumotachograph. The volume of the
high resistance path, together with its resistance relative to that
of the pneumotachograph is chosen such that, during respiration of
the patient employing the device, the high resistance path will
never be completely flushed through in one direction before flow
starts in the opposite direction. The high reistance path is chosen
to be a constant resistance such that the amount of flow
therethrough is proportional to the flow through the
pneumotachograph. Thus by sampling and analyzing a small portion of
the gas of the two chambers and measuring the amount of gas flow by
the pneumotachograph, the exact amount of oxygen uptake can be
calculated.
Inventors: |
Osborn; John J. (Tiburon,
CA) |
Assignee: |
Research Development
Corporation (San Francisco, CA)
|
Family
ID: |
25402733 |
Appl.
No.: |
05/894,189 |
Filed: |
April 6, 1978 |
Current U.S.
Class: |
600/531; 422/84;
73/863.61; 600/543 |
Current CPC
Class: |
A61B
5/0876 (20130101); G01N 33/497 (20130101); G01F
1/40 (20130101); G01F 1/36 (20130101) |
Current International
Class: |
A61B
5/08 (20060101); A61B 5/087 (20060101); G01F
1/34 (20060101); G01F 1/40 (20060101); G01F
1/36 (20060101); G01N 33/497 (20060101); G01N
33/483 (20060101); A61B 005/08 () |
Field of
Search: |
;128/2.07,2.08,2C,718,719,750 ;73/421.5R ;23/232R,232B
;422/83,84 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Cohen; Lee S.
Attorney, Agent or Firm: Flehr, Hohbach, Test, Albritton
& Herbert
Claims
What is claimed is:
1. Apparatus for use in a system for measuring oxygen uptake and
the like comprising first conduit means for conducting flow of
respiration gases to and from a patient, said first conduit means
including first flow resistance means, second conduit means having
one end thereof in communication with said first conduit means on
one side of said first flow resistance means and the other end
thereof in communication with said first conduit means on the other
side of said first flow resistance means, said second conduit means
including second flow resistance means, the volume of said second
conduit means being substantially greater than the volume of gases
conducted therethrough by a single breath of the patient whereby
flushing of the second conduit means is precluded, and sampling
means coupled adjacent the ends of said second conduit means for
analyzing the gases therein.
2. Apparatus as defined in claim 1 wherein said second flow
resistance means affords substantially greater resistance to the
flow of gases than said first flow resistance means.
3. Apparatus as defined in claim 1 wherein said first flow
resistance means comprises the flow resistance of a
pneumotachograph.
4. Apparatus as defined in claim 1 wherein said second flow
resistance means comprises an elongated tube.
5. Apparatus as defined in claim 1 wherein said second flow
resistance means comprises a series of elongated tubes arranged in
parallel.
6. Apparatus as defined in claim 1 wherein said second flow
resistance means comprises a housing having inlet and outlet ports
and an orifice membrane disposed across the interior of said
housing between said inlet and outlet ports, said orifice membrane
being formed of an elastic material, said orifice membrane defining
an orifice, a flap disposed within and substantially coextensive
with said orifice and having one edge thereof integral with said
membrane to thereby form a hinged connection between said flap and
said membrane, said flap including sides which converge to form the
narrowest portion of the flap at that portion thereof most remote
from the hinged connection to the orifice membrane, said hinged
connection being narrower than the widest portion of said flap.
7. Apparatus as defined in claim 1 wherein said first and second
flow resistance means each provide a constant resistance to the
flow of respiration gases over a wide range of flow velocity.
8. Apparatus as defined in claim 1 wherein said second flow
resistance means affords resistance to the flow of gases fifty
times greater than does said first flow resistance means.
9. Apparatus as defined in claim 1 wherein said second flow
resistance means affords resistance to the flow of gases one
hundred times greater than does said first flow resistance
means.
10. Apparatus as defined in claim 1 wherein said second conduit
means comprises a first chamber at one end thereof and a second
chamber at the other end thereof, said second flow resistance means
being disposed in communication between said chambers, said
sampling means being coupled to said chambers.
11. Apparatus as defined in claim 10 together with baffle means
disposed within said first and second chambers.
Description
BACKGROUND OF THE INVENTION
The direct measurement of oxygen uptake and respiratory quotient is
often of importance in medical research or medical care. Many
methods are available to make this measurement, but most of them
suffer from serious defects. To make the measurement directly from
the airway, it is necessary to know the respiratory minute volume,
and also the exact concentration of mean inspired gas and mean
expired gas for oxygen and carbon dioxide. The measurement of this
mean volume and of the two gas concentrations usually requires
bulky spirometers and other large apparatus, or else depends upon
high flow past the nose and mouth, with downstream sampling.
Alternately, the gas concentrations can be measured continuously
during inspiration and expiration with the measured concentrations
multiplied by the amount of flow and then integrated to obtain the
necessary values; but this requires a gas analyzer of extremely
rapid response and very careful control of all flows in the system.
Because of the careful control required such systems have not
proved very accurate.
SUMMARY OF THE INVENTION AND OBJECTS
The invention is incorporated in a pneumotachograph to which has
been added a sampling tube on each side of its resistance means.
Each tube is connected to a small chamber and the chambers are
interconnected by means of a relatively high constant resistance
path having a sufficient volume to prevent complete flushing
thereof in one direction before flow starts in another direction by
reason of the patient's breathing.
It is, therefore, a general object of the present invention to
provide an improved apparatus for measuring oxygen uptake and
respiratory quotient.
It is a further object of the present invention to provide such
improved apparatus for measuring oxygen uptake and respiratory
quotient which permits very accurate such measurements with
relatively inexpensive gas analyzers and at the same time without
the need of bulky or large apparatus to encumber the patient.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic diagram of apparatus for measuring oxygen
uptake and respiratory quotient in accordance with the invention
wherein the high resistance path incorporates a series of small
diameter tubes arranged in parallel;
FIG. 2 is a schematic diagram of another apparatus for measuring
oxygen uptake and respiratory quotient in accordance with the
invention but wherein the high resistance path is provided by the
use of an additional pneumotachograph;
FIG. 3 is a sectional view taken along the line 3--3 of FIG. 2, but
with the flap closed, showing the construction of the orifice
membrane of the additional pneumotachograph.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1 there is shown a pneumotachograph or sensing
head 11. Generally, a pneumotachograph is an instrument for
measuring flow by measuring the differential pressure across a
resistance in the line of flow. The resistance is constant over a
wide range of flow so that the pressure can be read directly as a
simple function of the differential pressure. The constant
resistance may be created by multiple parallel tubes sufficiently
small to maintain the flow laminar. Alternatively, the resistance
may be created by a moving orifice or other device, keeping in mind
that the resistance is to be constant over the range of flow.
The pneumotachograph 11 shown in FIG. 1 is substantially as shown
in applicant's co-pending application Ser. No. 779,557, filed Mar.
21, 1977, entitled "Variable Orifice Gas Flow Sensing Head" now
U.S. Pat. No. 4,083,245 which application and patent is
incorporated herein by reference. As set forth in that application,
the sensing head 11 is disposed in a gas flow line 13 through which
gas may flow horizontally in the direction of the arrows 15. The
head may include inlet and outlet portions 17 and 18 having ports
19 and 20 each of which carries a flange 21, 23 for securing them
together. An orifice membrane 25 is retained between the flanges
21,23 by means of screws 27 and the like. Flap 31 is joined
integrally with the membrane 25 and hinged at 33.
Pressure ports 35 and 37 are provided in the sensing head 11 and
are connected to a differential presure gauge 39 by means of the
tubes 41 and 43 so as to permit reading of the gas flow. The apex
45 of the orifice in membrane 25 is disposed at the bottom thereof
for easy passage of fluids which may be carried in the line.
While the pneumotachograph 11 set forth above is as described in
said U.S. Pat. No. 4,083,245 and is the preferred type of
pneumotachograph to be utilized in this invention, it is not
entirely necessary that this particular type pneumotachograph be
employed. Other constant resistance devices may be substituted.
In addition to the elements set forth above, there are two
additional tubes 47 and 49 connected to the pneumotachograph 11 on
opposite sides of the membrane 25 at openings 51 and 53 which are
disposed in the upper region of the pneumotachograph so as to avoid
interference with free fluids which may be carried through the
pneumotachograph.
Each of the tubes 47 and 49 connect with a small chamber 55,57 each
of which carries a series of baffles 59. The chamber 57 will be
employed to sample inspiration gases and the chamber 55 to sample
expiration gases.
The opposite ends of the chambers 55 and 57 are connected to the
opposite ends of a series of small parallel tubes 61. Tubes 61 are
chosen in size to collectively have a rather high resistance
compared to that of the pneumotachograph 11 and to individually be
of sufficiently small internal diameter (e.g. 3 mm.) that the flow
through it is laminar. In some instances it is satisfactory to
employ a single long loop of tubing rather than the multiple
tubes.
During the course of actual respiration flow passes alternately in
each direction through the pneumotachograph 11 and likewise flows
through the chambers 55, 57 and the tubes 61 alternately back and
forth at a fraction of the rate through the pneumotachograph 11. By
proper selection of the size of the tubes 61 and the chambers 55,
57 together with the assistance of the baffles 59 to retard mixing
in the chambers, the chamber 55 will always contain a sample which
is an average of the gas which is passed from left to right through
the pneumotachograph 11. The chamber 57 will always contain a
sample which is an average of the gas which is passed from right to
left through the pneumotachograph 11.
By means of taps 63 and 65 the gases in the chambers 55 and 57 may
be sampled and their composition determined. The composition of the
gas in the chambers 55 and 57 is an average of the expiration and
inspiration gases and sampling can therefore be done at a
relatively slow rate, the gas composition not changing rapidly over
several breaths.
It should be recognized that the resistance of the pneumotachograph
11 is constant over a large range of flow and may be designated
R.sub.1. The resistance of the tubes 61 is also constant over a
wide range since their small internal diameter causes a laminar
flow. This resistance may be designated R.sub.2. The number, size
and length of the tubes 61 are chosen such that R.sub.2 is much
greater than R.sub.1 and it has been found convenient to make
R.sub.2 fifty to one hundred times greater than R.sub.1. Flow
through the pneumotachograph 11 and tubes 61 are inversely
proportional to their respective resistances. Thus, if R.sub.2 is
one hundred times greater than R.sub.1, the flow through the
pneumotachograph 11 will be exactly 100 times the flow through the
loop 61 and the total flow will be 1.01 times the flow through the
pneumotachograph or one hundred and one times the flow through the
tubes 61.
With the above factors known for any specific embodiment of the
invention, it can be seen that calculation of oxygen uptake is an
easy matter. The total flow of gases can be calculated by known
means from the reading of the differential pressure gauge 39. The
quantitative composition of both expired and inspired gases can be
determined by connecting the taps 63 and 65 to a gas analyzer (as
shown with respect to another embodiment in FIG. 2) and multiplying
the readings thereof by a multiplier based upon the relative
resistance of the pneumotachograph 11 and tubes 61.
The actual sizes, volumes and so forth of the chambers 55 and 57
and tubes loop 61 may vary considerably with the expected
respiratory rate and volume. As an example, it may be assumed that
a particular patient expires about one liter per breath. If the
resistance of the tubes 61 is one hundred times the resistance of
the pneumotachograph 11, about 10 ml. will flow through the tubes
61 during each expiration. If the tubes 61 have a total volume of
about 50 ml. it will be seen that the expired gases will move
through the tubes 61 only about one-fifth of their length before
expiration is complete and the direction of flow reverses due to
inspiration. Thus, gases from the chambers 55 and 57 never
intermix.
The exact shape of the chambers or the configuration of the tubes
61, or even of the pneumotachograph are not important to the
invention. In fact the resistance of the tubes 61 can be supplied
by other means, including a pneumotachograph like element of very
high resistance such as set forth in FIG. 2.
In the embodiment shown in FIG. 2 elements identical to those of
the embodiment shown in FIG. 1 are identified with like reference
numerals and are not further described.
In the embodiment of FIG. 2 the high resistance can be provided by
an element 67, similar to a pneumotachograph but without lines to a
pressure gauge since flow rate therethrough need not be measured.
The resistance element includes an orifice membrane 68 shown more
clearly in FIG. 3 and more fully described in said U.S. Pat. No.
4,083,245. The resistance element 67 is connected to the tubes
47,49 through relatively elongated chambers 69 and 71 each of which
carries baffles 73. The baffles 73 serve the same purpose as the
baffles 59 in the embodiment shown in FIG. 1 and the resistance
element 67 serves the same purpose as the tubes 61. The size of the
resistance element 67 is considerably smaller than that of the
pneumotachograph 11 whereby its resistance is considerably greater
than that of the larger unit. Again, the path from the opening 51
through the chamber 69, resistance element 67 and chamber 71 to the
opening 53 has sufficient volume and includes sufficient baffles 73
that they are never completely flushed during a single breath. A
slug of gas moves back and forth through the pneumotachograph 67
with boundary interfaces somewhere within the chambers 69 and 71
but essentially never mixing in any large way with the gases in
those chambers.
To actually calculate the oxygen uptake samples are taken from the
chambers 69 and 71 through the taps 75 and 77, respectively,
leading to a gas analyzer 79 through a valve 81. It need only be
necessary to assure that the volumes drawn for sampling are
sufficiently small that there is no appreciable effect on the
concentration of the gases in the chambers 69 and 71.
The apparatus of the invention replaces the Douglas Bags and
spirometers of early methods and can be made very small and
portable. Even so the device of the invention gives valid samples
for measurements which are very reliable and do not require the use
of rapid gas analyzers. The invention provides a method for making
measurements which greatly reduces the bulk of the bags or tubing
required and the gas analyzers need have a response time of only
about 15 or 20 seconds. Moreover, the devices are simpler, lighter
and less susceptible to difficulty from saliva contamination and
leaks than are the devices of the prior art.
* * * * *